This present invention relates to digital image display, and more particularly to a method and apparatus for displaying a digital image on a display having a lower resolution than the image.
Digital images are often created or stored at high resolution. Many display devices, such as cathode ray tubes (CRTs) and liquid crystal displays (LCDs), may be unable to display an entire large, high resolution image all at once. For example, a scanned image several thousand pixels wide cannot be shown, without some manipulation, on an 800xc3x97600 pixel display device. Another example is a computer that generates a high resolution bitmap, based on running graphical applications, for output on a remote display that has a lower resolution.
Many methods have been devised for dealing with this problem. One common approach is to downscale the resolution of an image by a factor that allows the entire image to fit a lower-resolution display. This approach throws away information, often making the image difficult or impossible to comprehend, particularly if the image has graphical content like text.
A second approach is to display the original image data at the original resolution, however only displaying a subsection of the image at any one time. The entire image is not viewable at once with this methodxe2x80x94in order to view obscured portions, a user must manipulate a scrolling function to change the viewable portion of the image. This method typically employs xe2x80x9cscroll barsxe2x80x9d, which further decrease the viewable area of the image.
Yet another method allows the user to manipulate a xe2x80x9czoomxe2x80x9d function, alternating between a blurry view of the entire image and a legible view of a desired image subsection.
Finally, a fourth method uses two display windows. A first window displays a downscaled view of the entire image, and a second, non-overlapping window displays a subsection of the image at higher resolution. In order to use this method, a user must alternate their gaze between the first window, for selecting an area for display in the second window, and the second window, for discerning content. In addition to making viewing difficult, this method often results in the least efficient use of display space.
The present invention takes a different approach to displaying high-resolution image data on a low-resolution device. The present invention displays a subsection of the image data at its original resolution on one region of the display, but overlays this display on a larger, low-resolution display of the image data. The first region is registered to the second region, such that as the viewer focuses on a new area of the display, the first region xe2x80x9cmovesxe2x80x9d to align with the underlying downsampled image. The invention thus provides an intuitive and easy-to-use interface for viewing images on a limited-resolution display.
Thus in a first aspect of the invention, a method for displaying a digital image to a viewer is disclosed. Using an indication from the viewer of a desired point of interest on a downsampled version of an original image shown on a display (e.g., determined by active cursor or pointer position, or by an eye tracker), a point on the original digital image that is substantially registered with the point of interest is calculated. A subsection of the original digital image that includes this substantially registered point is mapped onto the display so as to overly the point of interest. Preferably, the subsection and the downsampled version are substantially registered at the point of interest.
In a second aspect of the invention, a display driver is disclosed. This driver includes a subimage extractor for retrieving a subsection of an input bitmap, according to supplied coordinates. It also includes a downsampler for calculating a downsampled version of the input bitmap. A mixer mixes the subsection and downsampled version onto a common display region, the position of the subsection on the display region being determined based upon the supplied coordinates.
In yet another aspect of the invention, a display system is disclosed. The system comprises a display device having a first resolution, and a video RAM memory having a size sufficient to store a bitmap larger than the first resolution. The system further comprises a display driver having a display mode for displaying a bitmap stored in the video RAM memory, where the bitmap is larger than the display resolution. In this display mode, a subsection of the stored bitmap is displayed on a subsection of the display device, and a downsampled version of the stored bitmap is displayed on areas of the display device other than the first subsection. The subsection is substantially registered to the downsampled version at a point on the display device.